Protective apparatus for electrical instruments.



No. 800,756. PATENTED OGT.3, 1905.

F. R. MUBERTY.

PROTECTIVE APPARATUS FOR ELECTRICAL INSTRUMENTS.

APPLICATION FILED DEC. 7, 1904.

2 SHEETS-SHEET 1.

PATENTED OCT. 8, 1905.

I. R. MQBEETY.

PROTECTIVE APPARATUS FOR ELECTRICAL INSTRUMENTS.

APPLICATION FILED DEC. 7. 1904.

2 SHEETS-SHEET 2.

UNITED STATES PATENT OFFICE.

-FRANK R. MoBERTY, OF EVANSTON, ILLINOIS, ASSICNOR TO WESTERN ELECTRIC COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS.

Specification of Letters Patent.

Patented Oct. 3, 1905.

Application filed December 7, 1904. Serial No. 235.856.

To all whom it Wtcty concern:

Be it known that I, FRANK R. MoBnR'rY, a citizen of the United States, residing at Evanston, in the county of Cook and State of Illinois, have invented a certain new and useful Improvement in Protective Apparatus for Electrical Instruments, of which the following is a full, clear, concise, and exact description.

My invention relates to protective apparatus for electrical instruments, such as telephone sets, and has for its object to provide reliable and certain means for protecting the user of such an instrument from injury from abnormal currents with which the circuit-conductors may be accidentally charged.

It is a common practice at the present time to provide telephone-lines in association with electric railways, and portable telephone instruments are furnished to be carried on the cars, these instruments being provided with flexible cords and switch-conductors by which they may be connected with the telephoneline at certain points along the route where connection switch-terminals are located. It has been found that the users of such portable telephone instruments have been frequently subjected to severe shocks from hightension circuits with which the telephone-circuits may be accidentally crossed. Such hightension currents will frequently break down the insulation and pass to earth through the body of the user of the telephone, who may receive the discharge either from the frame of the instrument which he is holding or from the flexible conducting-cord. The ordinary insulation of the cord will not be suflicient to prevent the discharge of high-tension currents, and this discharge may take place either to the other conductors of the cord or across theinsulating-coveringtotheuser. Thcpresent invention is specially designed to offer protection to the user of such an instrument.

My plan is, briefly, to provide a connectionswitch for a portable telephone which will complete a direct ground connection for one of the conductors of the flexible conductingcord leading to the metallic frame of the instrument, the switch being constructed to complete such ground connection before the other conductors are connected to the line. With this arrangement if the telephone-line should be charged with high-tension current such charge would not be transferred to the connecting-cond uctors of the portableinstrument until the frame and one conductor of the cord had already been grounded. Any discharge would therefore take place to said grounded conductor instead of through the body of the user. Preferably the extra conductor, which is thus arranged to be grounded to provide a direct path to earth, is wrapped around the other conductors, so that this grounded conductor is interposed between the user and the main circuit-conductors, which are liable to become charged to a dangerous potential.

I will describe my invention particularly by reference to the accompanying drawings, and the features or combinations which I regard as novel will be pointed out in the concluding claims.

Figure 1 is a diagram illustrating a portable telephone set and the circuits and apparatus for connecting the same with a telephone-line, the system being equipped with the improved means of my invention for protecting the user of the instrument. Fig. 2 is a detail view of a telephone instrument such as is often used in such portable sets, and Fig. 3 is a View illustrating the manner in which I prefer to assemble the conductors of the instrument in a flexible cord.

The same characters of reference are used to designate the same parts wherever they are shown.

Referring first to Fig. 1, a telephone set is shown provided with circuits and apparatus for connecting the same with a telephone-line running parallel with a trolley-line or other line carrying heavy currents, the system being equipped in accordance with my invention with means for protecting the user of the instrument from heavy currents due to crosses of the telephone-line with the trolley-lino. The telephone instrument may comprise a metallic frame at, carrying a receiver a at one end thereof and a transmitter a at the other end, the frame thus serving as a handle for the device. Circuit-conductors 1 2 lead from the receiver a of the instrument to the tip and contact pieces 6' Z2 respectively, of a movable connector or plug 6, a repeating-coil 0 being preferably interposed in said conductors to interrupt the continuity thereof as to direct current while maintaining the circuit of said conductors complete as to telephonic currents.

The transmitter (6 may be included in a normally open branch or shunt 3 of a portion of conductor 1 between the repeating-coil c and the telephone instrument controlled by a suitable switch (Z. This branch also includes a local battery 0 and the primary windingf of an induction-coil f, the secondary windingf whereof is included in the main circuit-conductor 2. Thus upon the closure of the switch (5 a local circuit for the battery (3 is completed, extending from one pole thereof over a portion of conductor 1, through the transmitter a, branch 3, winding f of induction-coil f, contacts of. switch (Z to the other pole of the battery.

An extra conductor 4: isassociated with the circuit-conductors 1 2 and may extend from the frame of the instrument to an extra or sleeve contact 6 of the said movable connector or plug 6, preferably beingwound spirally about the circuit-conductors 1 2 of the instrument, as shown. A lightning-arrester may also be associated with the circuit-conductors 1 2 between the repeating-coil and the movable connector, the plates g of said arrester being connected with the conductors 1 2, respectively, while the third plate g is electrically connected with the extra conductor 4.

The movable connector or plug?) is adapted to register with the stationary connectionswitch member or spring-jack it, connected with the telephone-line A. The spring-jack is provided with line-springs h 71 connected with the two limbs of the telephone-line, and an extra contact or thimble it, connected directly to earth. The telephone-line is shown in proximity to a high-tension line, such as a trolleyeline B. The two switch members Z) 71 are adapted in closing to unite the extra contacts If it first, thereby grounding the frame a of the telephone instrument before the circuit-contacts b b of the connector 6 register with the corresponding line-contacts h A? of the stationary switch member. Thus if the telephone-line A should be accidentally crossed with the trolley-line B, as indicated at X, the closure of the extra contacts (1" 7/ of the switch members Z) it will ground the extra conductor 4:, leading from the frame a of the instrument and surrounding the main circuit-conductors 1 2 of the cord, before uniting the said main conductors with the charged limbs of the telephone-line. The charge u pon the line if strong enough to break through the insulation of the conductors 1 2 of the instrument will take the direct path to earth by way of the extra conductor t without shocking or injuring the user of the telephone instrument. The lightning-arrester 0 also affords a means for diverting such dangerous current from the circuit-conductors 1 2 to the grounded conductor 1.

I prefer to employ a flexible cord for the telephone set, such as illustrated in Fig. 3,

having the several conductors of the instrument formed of Hat steel wire compactly arranged and assembled in the manner therein illustrated, the extra or grounding conductor being on the outside to constitute a grounded shield, so to speak, between the inner main conductors and the user of the instrument.

1 claim 1. The combination with a telephone instrument, oif circuit-conductors therefor, a telephone-line subject to crosses with higl tension circuits, a connecting-switch adapted to unite said conductors with said telephoneline, an extra conductor associated with said circuit-conductors and connected with the frame of said instrument, and a direct ground connection for said extra conductor completed in the closure of said connection-switch.

2. The combination with an electrical instrument having a metallic frame, of connecting circuit-conductors for said instrument, line-circuit conductors, a connection-switch adapted to unite said connecting-00mluctors to the line circuit, a protecting conductor connected with said metallic frame and wrapped about the circuit-conductors of said instrument, and means for establishing a ground connection for said protecting-conductor in the closure of said connection-switch, before said circuit-conductors are actually united thereby.

3. The combination with an electrical instrument, of a flexible connecting-cord therefor having circuit-comluctors and a protecting-conductor wrapped around said circuitconductors, a movable switch-connector at the end of said cord, having contact-pieces connected with said circuit-conductorsand an extra contact connected with said protectingeonductor, and a stationary switch member with which said connector is adapted to engage, said switch member having corresponding circuit-terminal contacts and an extra contact connected to earth, said switch members being adapted in closing to unite the extra contacts firstgwhereby the user of the instrument is protected from strong currents with which the circuit-conductors may be accidentally charged.

4:. The combination with an electrical instrument having a metallic frame, of a flexible coiiinecting-cord therefor having metallic circuit-conductors leading from said instrument and a spiral conductor connected with the frame of said instrument and surrounding said circnit-conductors, a plug having contacts connected with said circuit-conductors and having an extra contact connected with said spiral conductor, a spring jack with which said plug is adapted to register having circuit-tern'iinal contacts and an extra contact connected with earth, said last-mentioned contact being arranged to register with the corresponding extra contact of said plug before the circuit-terminal contacts of said plug and spring-jack are united, substantially as described.

5. The combination with a telephone instrument, of a flexible cord for said instrument having circuit-conductors connected with said instrument, and a spiral conductor connected with the frame of said instrument and surrounding said circuit-conductors, a movable connector having contacts connected with said circuit-conductors and having an extra contact connected with said spiral conductor, a stationary switch member having circuit-terminal contacts and an extra contact connected to earth, a telephone-line subject to crosses with high-tension lines connected with said circuit-terminal contacts of said switch member, the said switch members inclosing being arranged to unite the said extra contacts first, whereby the user of the instrument is protected from strong currents with which the line may be accidentally charged.

6. The combination with atelephone instrument comprising a metallic frame having a receiver and transmitter mounted at opposite ends thereof, of a flexible connecting-cord for said instrument having metallic circuitconductors connected with said receiver and transmitter and a spiral conductor connected with the frame of said instrument and surrounding said circuit conductors, a plug having tip and ring contacts connected with said circuit-conductors and a sleeve-contactconnected with said spiral conductor,a springjack with which said plug is adapted to register, comprising line-springs adapted to register with the tip and ring contacts of said plug and a thimble connected to earth, said thimble being adapted to register with the sleeve of said plug before the line-contacts of said plug and spring jack are united; whereby the user of the telephoneinstrument is protected from strong currents with which the line conductors may he accidentally charged.

7. The combination with a telephone instrument having a metallic frame, of a movable terminal connector, a pair of main conductors connected with the instrument, at protectingconductorconnected with the frame of the instrument, said movable terminal connector having contacts connected with said main conductors and an extra contact connected with said protecting-00nductor, a stationary switch member with which said connector is adapted to engage, said switch having line-contacts and an extra contact connected to earth, said switch members being adapted in closing to o1n said extra contacts before uniting said line-contacts, and a lightning-arrester having a plate connected with each line conductor of said instrument and a third plate connected with said protecting-conductor; whereby the user of the instrument is protected from strong currents with which the line conductors may be accidentally charged.

In witness whereof I hereunto subscribe my name this 23d day of September, A. D. 1904.

FRANK R. MOBERTY. Witnesses:

FREDERICK l. MolN'rosii, E. F. BEAUBIEN. 

